Even though here in Austin we don’t have a lot of days when heat is needed, I think that I do need a functioning heater in the truck. For one thing, I might need to be able to blow hot air on the windshield if it starts to fog up.
So, I removed the original hot water heater core and modified it by adding an electric ceramic heater element. Keep reading for the details …
To create an electric heater, I took a ceramic heater core from an electric space heater and inserted it into the existing hot-water based heater core from the truck. The ceramic heater cores are readily available. Since they are just resistors, they will work on AC (house) or DC (truck battery pack). And I understand that the resistance increases as they get hotter so they are somewhat self protecting (I have not tested this myself).
I will use a relay to switch the traction battery pack voltage to the electric heater. I think I have figured out how to wire it in with the existing ventilation system wiring so that it will only heat if the fan is turned on which helps keep me from burning stuff up.
First of all, I don’t want to take credit for this method. I have seen several web sites that used a variant of this method so I studied to see what other people have done, and then created my own solution.
To start, I obtained a cheap electric space heater from Amazon for about $20. Here is the one I used, but I think that most of the 1500w ceramic space heaters use a very similar element, so almost any would do.
Here is what the heater core looks like after it has been removed from the housing. When I removed it, I cut the wires as long as possible. Also, there is a thermal circuit breaker in the housing next to the heater element, so I also saved this to use later. You can see it attached to the brown wire on the right in the photo below.
Next, I laid the element on top of the original hot-water heater core that I earlier removed from the truck. I traced the outline just by gouging the fins a little bit with a screwdriver, so I can see where to cut.
I then cut a rectangular piece out of the center of the original heater core. I have read about various techniques to do this, but I just used a 4-½ inch angle grinder with a metal grinding wheel. It made short work of the heater core and went right through it. I had to use a hacksaw blade to finish out the corners and make them square.
Here is what it looks like after I cut the hole in the heater core.
And here, I laid the ceramic element in the heater core to test fit.
I wondered about how to handle the wires, and then I noticed that the original piping that was used for water came out the side, and it was the perfect size for routing wires. So I drilled out one of the original water pipes (inlet or outlet, I don’t know).
Here is the ceramic element, test fit again, this time showing how the wires will be routed. By routing the wires this way, they will come out of the heater core the same way as the original hoses, which means I can just insert this back in the dash where it came from without needing any modifications to anything under the dash.
Okay, next question, how is the ceramic heater element attached to the original heater core. I have seen several solutions. One was to make a metal plate that covers the heater core and has places to screw the heater element. Another was to use high temperature silicon.
I decided to try JB Weld. It is a very strong epoxy that can handle high temperatures. I have to say that before this experience I really had not used JB Weld before, but I have to say, that stuff is magical and I will be sure to keep some on hand from now on.
It took me three “epoxying” sessions to get this finished. First I covered one side of the heater core with a piece of plastic and then laid it with the plastic side down. This allowed me to place the ceramic element in the hole and then I squirted JB Weld all around the edge. Once this cured, the ceramic element was securely glued to the heater core.
The next problem is that now there is a gap where the wires are connected to the heating element (take a look at the photo above). I need some way to cover this. I thought about a piece of plastic, or maybe using some metal sheeting. I was worried about the temperature limitations of the plastic, and the electrical conductivity of a metal sheet. Then I thought about trying to make a piece out of JB Weld. I found a piece of plastic packaging that almost the perfect size to use as a form, and I “cast” a piece using JB Weld.
Now that I can block off the area of the wiring, the last issue is how to force all the air through the ceramic element and to not bypass it by flowing through the remaining section of the heater core. JB Weld to the rescue again. This time I mixed some up and “painted” it on the fins, effectively sealing them up.
All of this took me about 3 sets of JB Weld, which was about $15. The photo below shows the finished result. You can see the ceramic element glued in the center. The messy edge is because I did not have a tight fit when I poured the original JB Weld and it oozed out past the surface. But this is only cosmetic and does not affect the function. In the photo you can also see the piece that I cast, and the JB Weld covering the remaining original heater core.
Here is another photo from the other side.
Since I took the last photo, above, I have also added the thermal circuit breaker from the original space heater. I attached it to the wiring with zip ties. This will be the inlet side, so as long as air is flowing it should remain cool. But if air stops flowing and the heater element is still on, it should heat up the thermal breaker pretty quickly and cut power to the heater element.
2013/02/13 at 21:40
I have since discovered what happens when you try to break a circuit that has DC current at high amps. If the switch is not meant to break DC current it tends to arc and melt things. Therefore I doubt that the thermal breaker will work the way I intended. It may break once but will be ruined after that, or it may not break the circuit at all. Lets hope I don’t need it because I have no plans to take it apart and redo it now.